An arrangement of this type is known from EP 0 386 033 B1 or the technical manual SIEMENS: “Prozess-Gas-Chromatograph MicroSAM”, [Process Gas Chromatograph MicroSAM] Edition 4.01 C79000-G5300-C560-4.1, pages 30, 31, 40 and 41, on the internet: http://cache.automation.siemens.com/dnl/jQxMTYyMwAA—17969517HB/MicroSAM% 2DManual D V41.pdf (Sep. 07, 2006).
In gas chromatography, the performance of the analysis of gas samples largely depends on the sample being introduced into the chromatographic separator (separating columns or separating column circuits). Small metered amounts in the form of short and as sharply restricted “slugs” of sample gas as possible are conveyed in the carrier gas path, which conveys the sample slug to the separator and herethrough.
To this end, the afore-cited known arrangements have a sample gas path and a carrier gas path, which are both connected to a carrier gas source with constant pressure. A controllable metering device is arranged between the carrier gas source and the sample gas path, said metering device consisting of valves and a metering loop and being used for feeding a wide, unsharp sample gas slug into the carrier gas stream through the sample gas path. A device for introducing different pressures into the sample gas path and the carrier gas path allows a small metered amount to be extracted from the sample slug in the sample gas path by way of a connection gas path between both gas paths and to be conveyed into the carrier gas stream through the carrier gas path. From there, the now short and sharply restricted sample slug reaches the separator.
The introduction of the different pressures in the sample gas path and the carrier gas path is effected for instance by means of a switchable valve in the carrier gas path between the carrier gas source and the branch of the connection gas path, with a first adjustable flow resistance being arranged in the sample gas path upstream of the branch of the connection gas path and a second flow resistance being arranged therebehind. The flow resistances are used to determine the pressure conditions in each of the two positions of the valve and thus to prevent sample gas from leaving the sample path in the carrier gas path unintentionally for instance.